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A1-L10 Phase Boundaries and Anisotropy Via Multiple-Order-Parameter Theory for an FCC Alloy



G B. Tanoglu, Richard J. Braun, John W. Cahn, Geoffrey B. McFadden


The dependence of thermodynamic properties of planar interphase boundaries (IPBs) and antiphase boundaries (APBs) in a binary alloy on an FCC lattice is studied as a function of the orientation of their normal with respect to the underlying lattice. Using a recently-developed diffuse interface model based on three non-conserved order parameters and the concentration, and an improved free energy density that gives a realistic phase diagram with one disordered phase and two ordered phases such as those that occur in the Cu-Au system, we are able to find IPBs and APBs between any pair of domains and phases, and for all orientations. The model includes bulk and gradient terms in a free energy functional, and assumes that there is no mismatch in the lattice parameters for the disordered and ordered phases so that elastic effects can be neglected. The bulk energy model is based on the multi-atom interaction among at least four neighbors, and the entropy term is taken as due to ideal mixing on each sublattice. In this paper, we set up the governing equation and give a catalog which constitutes the sets of boundary conditions for all IPBs and APBs. We then focus on one specific set as an example, the IPB between the disordered A1 phase and the L10 ordered phase, which could not be calculated with the free energy used previously. For this IPB we compute the numerical solution of the boundary value problem to find its interface profile, its interfacial energy as a function of orientation, temperature, and chemical potential (or composition).
Interfaces and Free Boundaries
No. 3


antiphase boundaries, Gibbs adsorption equation, order-disorder transitions, phase diagrams, surface energy


Tanoglu, G. , Braun, R. , Cahn, J. and McFadden, G. (2003), A1-L1<sub>0</sub> Phase Boundaries and Anisotropy Via Multiple-Order-Parameter Theory for an FCC Alloy, Interfaces and Free Boundaries (Accessed June 17, 2024)


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Created August 31, 2003, Updated October 12, 2021